1. Field of the Invention
The present invention relates to electrostatographic copiers and printers, and more particularly, to a mechanism for responsively and precisely spacing the development roller of a development apparatus from the image-bearing surface of a copier or printer.
2. Background of the Invention
The process of producing or reproducing copies of images in an electrostatographic copier or printer involves moving an imaging member, in the form of a rigid drum or flexible web, past a series of process stations. As this occurs, the imaging member is first charged, and then imagewise exposed to form a latent electrostatic charge image thereon. The latent image is thereafter developed or made visible by moving it past a development station or apparatus where charged, pigmented toner particles, from development material held in a sump portion at the development station, are attracted to the latent image charges. The developed or toner image is subsequently transferred, at a transfer station, to a suitable receiver, such as a copy sheet of paper which is thereafter advanced through a fusing station. At the fusing station, the toner particles on the copy sheet, particularly those forming the desired image, are heated and fused. Meantime, any particles remaining on the imaging member are thereafter removed, at a cleaning station using a cleaning apparatus such as a fiber brush, prior to again reusing the imaging member as above to form and transfer images.
The development material being held in the sump portion at the development station or apparatus may be single component in that it consists entirely of toner particles, or it may be multiple component. Multiple component, for example two-component developer material may consist of an admixture of toner particles and carrier particles. Where the development station or apparatus is holding multiple component developer material, the carrier particles are usually stirred together with the toner particles in order to triboelectrically charge both types of particles.
The charged developer material, consisting of such charged particles, is then moved within the development station by means including a development roller so as to bring the toner particles into transfer proximity with the latent image on the image-bearing member. The resulting transfer of the toner particles to the image on the image-bearing member constitutes the development step of electrostatographic process as described above.
As is well known in the art, the effectiveness and quality of such image development depends, in great part, on the preciseness and constancy of the spacing between the surface of the development roller and that of the image-bearing member.
As disclosed in commonly assigned U.S. Pat. Nos. 4,926,198, issued May 15, 1990, and No. 4,806,991, issued Feb. 21, 1989, it is well known to use back-up rollers or ski rods on the backside of the image-bearing member for positioning the image-bearing surface thereof at a desired spacing from the development roller of a development station or apparatus. Typically, a pair of parallel back-up rollers or ski rods is used. The rollers or ski rods are rotatable and are frictionally rotated by the moving image-bearing member. The development apparatus containing the development roller usually is mounted on float means such as springs, and mechanically positioned so as to be precisely spaced from the plane of the image-bearing member.
Unfortunately, however, undesirable variations will occur in the positioning of the plane of the image-bearing member as formed by the back-up rollers or ski rods. Such variations may be due, for example, to the ski rods being out of parallel with each other, or to a tilt or skew therein caused by the moving image-bearing member or film. If not corrected as precisely as possible, such variations will, of course, result in non-uniform and, hence, poor quality toner image development. Furthermore, if such variations are not corrected, they will detrimentally affect the effectiveness of a DPU scavenging device that is positioned as disclosed in related U.S. application Ser. No. 07/597,135, filed here on even date in the name of the same inventor, and entitled "DEVELOPMENT APPARATUS HAVING A PLATE SCAVENGING DEVICE".